Unless your hunting varmits, you can't hunt with a 20-30 round mag. They do make 5 round mags for hunting. Both AK(7.62x39) and AR(.223 Rem) type rifles are just fine for hunting provided you don't try any really long shots. Neither has much power at over 100 yards.
I got curiuos about the largest game taken with an AR-15: Polar bear!
The bear was rampaging in a small town. The shooter only had his AR-15 with him. He killed the bear but emptied the full 20 round clip. Not a reccomend practice unless you want to live fast and die young.